1. Technical Field
This invention relates generally to the batch processing of miniature electronic circuit components, including passive, two-terminal, ceramic capacitors, resistors, inductors, and the like. More particularly, it concerns a vacuum ring and a test plate that are used on a component testing system for holding such components or other type of device under test (DUT) as part of the batch processing for purposes of parametric testing.
2. Description of Related Art
The tiny size of electronic circuit components of interest herein complicates processing. Typically fabricated of ceramic material in parallelepiped shapes having dimensions as small as 0.020″ by 0.010″ by 0.010″ more or less, these difficult-to-handle components require appropriate equipment and precision handling techniques. During testing, such a component is sometimes referred to as a device under test (DUT).
U.S. Pat. No. 6,194,679 describes a testing machine for such DUTs. The testing machine in that patent is similar in some respects to the testing machine available from Electro Scientific Industries, Inc. (ESI) of Portland, Oreg. as its model ESI-3300. Among other things, the testing machine includes a component-holding part that is referred to herein as a “test plate” and a vacuum-communicating part that is referred to herein as a “vacuum ring.” The test plate is mounted rotatably over the vacuum ring where it functions as means for receiving and hold a batch of DUTs. The vacuum ring (sometimes called a vacuum plate) couples a vacuum to the test plate that helps hold the test plate and load the DUTs onto the test plate. As the test plate rotates relative to the vacuum ring, various test are performed. After testing, DUTs are blown out of the test plate into various containers according to the test results.
Although effective in many respects, there are some concerns related to the vacuum ring and the test plate. One is wear. Ceramic powder and loose ceramic pieces from DUTs can abrade the surface of the vacuum ring that faces the test plate. The vacuum ring, typically fabricated of nickel-plated steel, must eventually be replaced as a result (as much as two or three times a year).
In addition, testing may involve voltages on the order of 1000 volts. Various forms of grease, grime, dirt, dust and other electrically conductive material on the vacuum ring and/or on the insulation material around the lower contact provide unwanted conductive paths. Arc-overs occur, and repeated arc-overs can damage the vacuum ring and even the expensive power supplies.
DUT size differences introduce another concern. The vacuum ring includes what are referred to as eject holes or blow holes that are formed in the vacuum ring by milling, drilling, or other mechanical process. Compressed air coupled to an eject hole at just the right time serves to blow a DUT from the test plate into a sorting box according to test results. But, different size DUTs require different pressure (i.e., blowout force). Little DUTs require little eject holes for less blowout force while bigger DUTs require bigger eject holes for greater blowout force. As a result, various vacuum rings must be kept available and substituted on the test machine according to DUT size.
Each of these concerns adds time and expense to DUT testing. Thus, a need exists for an improved vacuum ring and test plate construction so that the vacuum ring is more abrasion resistant, the vacuum ring is more arc-over proof, and differing DUT sizes are better. accommodated.